With respect to processes for the storage of gases, the development of highly porous materials, for example hydrogen, natural gas, etc., by means of adsorption, are the object of recent research. To date, gas absorption storage systems exist only for applications utilizing metal hydride powders wherein, for example, hydrogen molecules are split and the protons are bound chemically to the host material or stored in intersticial sites of the metal lattice, also called hydrogen (H2) absorption or hydriding. Applications (e.g. for vehicles and submarines) involve large pressure vessels with chambers containing the metal hydride powders. Heat exchangers are located inside the storage vessel, since during the absorption process heat energies of typically 30 kJ/mol H2 are produced. A hydrided material normally expands by 20% to 30% in volume compared to its initial state. Thus, the problem of expansion/shrinking of the host material during operation also has to be resolved (e.g. by using compartments connected to springs).
With respect to adsorption processes for the storage of gases, highly porous gas storage materials suitable for adsorption and desorption of gases are known in the prior art. Such materials are, for example, activated charcoal, metal organic frameworks (MOFs and MILs), nano-cubes, coordination polymers (CPs), prussian blue analogues, or polymers of intrinsic microporosity. A description of highly porous gas storage materials can be found in the articles written by Professor Yaghi of the University of Michigan, published in Science magazine. (Systematic Design of Pore Size and Functionality of Isoreticular MOFs and Their Application in Methane Storage, Science Vol. 295, 18 Jan. 2002; Hydrogen Storage in Microporous Metal-Organic Frameworks, Science Vol. 300, 16 May 2003). Also, in a press release by Dr. Ulrich Muller, of BASF, 28/29 10, 2002, “Nano-cubes for Hydrogen Storage” MOFs are described here as “Nano-cubes”. Highly porous polymers suitable as gas storage materials are also described in an article in Materials Today, April 2004, “Microporous Polymeric Materials”. All these highly porous gas storage materials have surface area densities from 3,000 m2/g (activated charcoal, MOF5) to more than 4,500 m2/g (MOF177, NATURE, Vol. 427, 5 Feb. 2004, “A Route to High Surface Area Porosity and Inclusion of Large Molecules in Crystals”). Recently developed MOFs (MILs), such as nano-cubes, have shown surface area densities greater than 5,000 m2/g, ie., MIL 101 with 5,600 m2/g (MIL-101 is a new, unusually porous material whose unit cell has an unprecedented volume of about 702,000 cubic Angstroms, meaning that the solid is about 90% empty space once the solvent molecules normally filling its pores are removed. It also boasts pores that are 29 or 34 Angstroms across and an internal surface area of 5,900 m2/g (Science 2005, 309, 2040).
Due to their high porosity (typical mass densities ranging from 0.3 to 0.6 g/cm3) and high surface area, highly porous gas storage materials could be used for the storage of gases, such as methane and hydrogen. The gas is adsorbed (using very weak van der Waals forces) on the large surface areas as a monolayer (for moist cases). These highly porous gas storage materials are usually fine powders. To increase the volumetric density, they could be compressed to be formed into fine or course granulated material (pellets). This granulated material has a higher mass density, eg., about 0.7g/cm3, but also an up to 30% reduction in the surface area. These highly porous gas storage materials may be filled into a pressure vessel. The heat generated during the adsorption process (adsorption energy between about 3and 6 kJ/mol H2 with MOFs and about 6 kJ/mol H2 with activated charcoal) should be compensated by a heat exchanger. There may be ambient temperature and cryogenic operation modes depending on the gas, for example H2 or natural gas.
The stored gas is removed from the vessel by desorption. Desorption occurs by a reduction of the gas pressure and by a suitable supply of heat energy. The supplied and exhausted heat energy is greater than the adsorption/desorption energies.
Gas adsorption technologies are currently used mainly for gas purification purposes (e.g. Pressure Swing Adsorption) rather than for storage and retrieval of gases by adsorption and desorption, respectively. A typical purification application in the automotive industry is a purge container connected to gasoline or diesel fuel tanks. These containers intermediately capture and store evaporated hydrocarbons from automobiles for the control of diurnal and hot soak conditions as well as in the more demanding fuel filling cycle.
Also, simply filling a pressurized vessel with a highly porous gas storage material does not meet optimal gas flow and heat removal requirements. A structured arrangement of the highly porous gas storage material is necessary for optimized adsorption and desorption of the stored gas.
Furthermore, although storage systems utilizing metal hydride powders for gas absorption are known, there are currently no storage systems or apparatus available for optimal adsorption and desorption of gases utilizing highly porous gas storage materials.
Accordingly, what is needed in the art is a storage system or apparatus for optimal adsorption and desorption of gases utilizing highly porous gas storage materials.